In the spinning of filaments from thermoplastic synthetic resins, it is known to force a thermoplastic synthetic resin through the orifices of a spinneret, thereby generating a curtain of filaments. These filaments can be collected on, for example, a perforated surface below which suction can be generated to produce a jumble of such filaments in the formation of so-called spun bond fleece. The collecting surface may be a conveyer and the fleece which is thus formed can be calendared with the filaments being bonded randomly to one another, e.g. by fusion at the temperature of the filaments. In the production of spun bond fleece, the filaments are usually drawn, e.g. by entrainment in a process air flow and can be cooled between their emergence from the spinneret orifices and their collection on the perforated surface. Another method of forming a fleece from filaments generated in a spinneret is the melt-blown process, whereby the filaments are away from the spinneret torn and from fibers as the filaments merge from the spinneret and the fibers are collected on a perforated surface which can be a conveyor.
It is also known to produce such filaments as bicomponent filaments from two different synthetic resins, thereby gaining advantages of both. For example, the spinning of bicomponent filaments with a core/sheath structure from two different thermoplastic synthetic resins has been taught in DE 37 10 946 A1. The filaments have a core usually of one synthetic resin surrounded by and bonded to a sheath of the other synthetic resin and may have advantages of both. For example, the core synthetic resin can contribute greater strength whereas the sheath synthetic resin can contribute surface characteristics which maybe desirable. In any case, the filaments have advantages which cannot be obtained with either of the two synthetic resins alone.
In practice it has been found that the nozzle or spinneret system required for producing such core/sheath filaments is relatively expensive and not always suitable for use in the production of spun fleeces or webs, especially because the bicomponent filaments cannot be produced with total uniformity throughout the filament curtain and because there are differences in the characteristics of the filaments from one filament group to another.
It is important that the filaments have more or less uniform characteristics over the entire array of spinneret orifices and especially over the entire width of the fleece which is to be produced. Reference may also be had to DE 37 38 326 C2.